MOON TOWNSHIP, Pa. — Republicans mounted a last-ditch stand here to save their struggling candidate for a House seat deep in the heart of Trump country, unleashing the party's full arsenal to stave off a major embarrassment for the president and GOP heading into the midterms.

Nearly every corner of the national party was involved in the final push over the weekend — from the Republican National Committee, which deployed staffers from Washington to knock on doors; to a cash-flush GOP super PAC that orchestrated an under-the-radar effort to diminish Democratic hopeful Conor Lamb’s standing with liberal voters; to the powerful Koch political network, which is spending hundreds of thousands of dollars on a mail and field deployment campaign ahead of Tuesday’s closely watched special election.

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And then there was President Donald Trump, who flew here on Saturday evening to campaign with Republican nominee Rick Saccone, an appearance the White House hopes will energize GOP voters who’ve yet to rally behind the underperforming candidate.

The multimillion-dollar undertaking underscored the enormous stakes for the party in the southwestern Pennsylvania district, which Trump won by 20 points but where polls show Lamb and Saccone locked in a tight race. A loss here would be an ominous sign for the party in the run-up to November, starkly illustrating its softening support even in Trump strongholds.

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It would also raise questions about whether the themes the GOP has thrust to the forefront of the race — namely its tax cuts and opposition to House Minority Leader Nancy Pelosi — are as potent as the party had hoped.

By the end of the weekend, Republicans had dropped more than $8 million on TV ads, outspending Democrats nearly 2 to 1, according to media buying figures. In an indication of just how much capital the administration is expending on the contest, Donald Trump Jr. is slated to campaign with Saccone on Monday, two days after his father staged a rally.

As the contest hurtled into its final days, Lamb, a square-jawed 33-year-old Marine veteran and former federal prosecutor who has appealed to voters in both parties, presented himself as a consummate underdog. Addressing a standing-room-only rally at the Greene County Fairgrounds in Waynesburg on Sunday afternoon, Lamb said the grass-roots support he’d received had allowed him to withstand the advertising barrage from Republican-aligned outside groups.

“They use these same tactics everywhere around the country, but I think when they came to western Pennsylvania, they weren’t counting on what they were going to find here,” he said.

At a rally with Lamb at the United Steelworkers headquarters in downtown Pittsburgh on Friday, Democratic Rep. Mike Doyle, the dean of the state’s congressional delegation, marveled at how much Republicans had spent on the race.

“The president comes in for his second visit, the vice president has been here, Ivanka’s been here, Cabinet secretaries have been here, 10 kitchen sinks has been thrown here, $15 million has been spent here, and that Marine is still standing,” Doyle exclaimed.

Yet there’s evidence the Republican offensive might be having some effect. A data analysis completed by the RNC during the middle of last week showed Lamb leading just 48 percent to 47 percent, according to two people briefed on the numbers. The Democrat’s advantage had shrunk from 4 percentage points in the committee’s previous analysis of the race days earlier.

Saccone, a 60-year-old state legislator and retired Air Force officer, was optimistic that momentum was “swinging our way.”

“It’s a special election, so it’s all about turnout,” Saccone said at the Allegheny County Republican Party headquarters on Friday, when he was asked why the race was so close. “Our people get out, we win, and there’s no problem.”

But Saccone vented frustration at the media for their coverage of the race, saying they had given Lamb flattering coverage while largely ignoring Saccone‘s accomplishments.

“The media fawns over my opponent, trying to stretch his little thin résumé and trying to make it sound like it’s something big, when I have a big résumé that they try and scrunch down and don’t say anything about,” he said.

Senior Republicans have called Saccone a lackluster candidate who has heavily leaned on the national party to run his campaign. Trump himself has been down on Saccone in private; at the rally, the president tried to gin up some excitement for him.

Trump described Saccone as a “really good person,” told his supporters to “go out on Tuesday and vote like crazy,” and highlighted his decision to impose tariffs on imported steel and aluminum. Party officials hope the tariffs announcement will win over labor workers in the union-heavy district.

At the same time, Republicans are trying to dampen Lamb’s support among liberals, whom he needs to show up in big numbers in order to win. Congressional Leadership Fund, a House GOP-aligned outside group, sent mailers to liberal households in the district outlining Lamb’s pro-gun credentials and his support for the Second Amendment.

Lamb was concerned enough about the GOP maneuver that late last week he launched a TV ad to explain his views on guns. The commercial said Lamb “supports strengthening background checks to keep guns from criminals and people in need of mental health treatment.”

As they funneled into Trump’s rally on Saturday, some of the president’s supporters conceded they were worried. They said Lamb had waged a surprisingly energetic campaign for such a conservative district.

“I’ve seen a lot more Conor Lamb signs in my neighborhood,” said Tracy Barzan, a 45-year-old stay-at-home mom whose 13-year-old son, Gavin, wore a Trump hat signed by Mike Pence.

“A lot of people I’ve heard from who are voting for Conor Lamb are doing so because of his age, him being younger, and looking at it that he has fresh ideas,” she added.

A loss on Tuesday would be a painful blow for Republicans, given the pro-Trump tilt of the district and the importance the president has placed on Pennsylvania. The state was a keystone of Trump’s 2016 electoral coalition, and he has visited a handful of times since his inauguration.

Before his visit on Saturday, some of the president’s loyalists questioned whether Trump should skip the campaign event, worried that he'd take even more blame if Saccone loses. But others argued the president had little to lose.

“If Rick Saccone somehow loses on Tuesday, regardless of whether the president made the trip on Saturday or not, the media will blame the president,” said David Urban, who oversaw Trump’s 2016 campaign in the state. “It reminds me of, ‘Heads I lose, tails you win.’”